Method of forming taps



Patented June 24, 1941 UNITED STATES PAT @FFI-CEv METHOD F FORMING TAPS Glen H. Stimson.. Royal Oak, Mich., assigner to Greenfield Tap. and Die Corporation, Greenfield, Mass: a corporation of Massachusetts l 'originar application April 27, 193s, serial No. 204,489. Divided and thi'sapplicatlon Novemy ber zu; rasa-.Senn No. acacia iciaim.y (ci. :1i- 288) This invention relates to threading taps andv particularly to` taps ofthe type generally known as gun taps in which the main flutes merge at the entering endl with auxiliary or" gun flutes extending at an angle. This arrangement provides: an angled series of cutting teeth which project the chips forwardlyl along the gun flute and ahead o-f the tap. 'A tap of this type is shown in the patent to Wells, No. 1,165,822;

The general purpose ofthe invention is to improve the 'chip cutting and dischargingv action of a gun tap. More specica-lly,'the invention includes improvements in the contourl and relative angles of attack of the cutting teeth, the contour and surface of thegun flute, and theprovision of means and methods'for producing; the desired construction and arrangement.

Other objects and advantages off' the invention,

including the construction andrelative arrange. ment of parts, will appear,from` the following description considered in vconnection with the accompanying drawing, in which,

Fig. 1 is a side View of a gun tap with parts broken away;

Fig. 2 is an end view from the leftfof'Fig'. 1 on an enlarged scale, showing the position of a grinding cylinder; Y

Fig. 3 isY an enlarged fragmentary side view of the enteringv end of a guntap indicating" the position of the grinding cylinder` and' a grinding Wheel; Y

Fig. 4 is a View similar to Fig. 2 indicating the position of a conical grinding wheel;

Fig` 5 is similary to Fig. 3, likewise 'showing theconical` grinding wheel;

Fig. 6 isla View similar'to Fig. 2 showing a dii'- ferent arrangement, and

Fig. 7 is a transverse sectional view of the tap shown in Fig. 3 indicating the rake angle of the cutting teeth.

The gun tap I I includes the usual tap structure comprising shank I2 and lands I3 carrying leading threads I4 and cutting threads I5, which are shown as taper ground. Lands I3 are separated by the main longitudinal flutes I6 which are arcuate in cross section.

Each main flute I6 merges with a gun flute II extending downwardly from the main flute to the entering end of the tap when viewed as in Fig. 3. Each gun flute I1 extends across the entering ends of cutting threads I5, the angle between the surface of flute I6 and the radius from the axis of the tap to the apex of said end of a thread I5 constituting the rake or angle of attack of said thread as illustrated at alpha and beta in Figs.

2, iv and 6. Assaid ends constitute the cutting instrumentalities of the tap they will be referred to herein for convenience as teeth I8.

With the arrangement shown inv Figs. 2 andi 3-,

' the downward' inclination of the ute II' toward the tap end producesy a progressively increasing width of the cylindrical portion of said flute, carrying teeth I 8 progressively higher on-v the cylinder surface and therefore increasing corr-e-Y spondingly the rake of said teeth. As illustrated in Fig. '1 the rake ang-le of the cutting edge of the teeth i8. is the angle between the radius of the axis of the tapf and the surface of the gunute I'E at the apex ofthe tooth. This is to a certain extent balanced by the progressively reduced diameter of threads I5 due to the taper grindwhere the tap is of this type; but in gen-v era-l, and in the arrangement shown, the rake of teeth7 I8- will still be progressively greater toward the tap end As illustrated in- Fig'. 2 the threads at the tap endl have arakealpha of substantially 35' while the threads at the root o-f the taper have a' ralie-vl beta of about 27. u

Thegun ute I'I may be formed by a milling cutteror disk grinding wheel havingy a cutting faee'that` is send-circular in cross section, travel'- ing longitudinally' of the tap in a suitable path,

the path of the semi-circular edge portion ofthev forming device corresponding to the lowerv half of'` the above mentioned cylinder. A marginal portion of a properly positioned vdisk grinding Wheel I9 of this' type is indicated in Fig. 3.

This method of' forming the gun flute tends to produce relatively inconspicuous but de'nite grooves and ridges extending longitudinally along the flufte. While these grooves and ridges are-'so slight as tobe apparently inconsequential in the operation ofthe tap II, it has been discovered that if the gun utes I'I are ground or polished so as to destroy the longitudinal grooves and ridges, the action of the tap in cutting and discharging the chips in the manner characteristic of such taps is materially improved. An improvement in such operation is`likewise produced when similar relatively slight grooves or ridges 2U extend in a generally transverse or circumferential direction in gun flutes I'I, as indicated diagrammatically in Fig. 1.

'Ihese results may conveniently be obtained by means of a cylindrical polishing or abrading tool such as the cylindrical grinding wheel 2| indicated in Figs. 2 and 3, the diameter of which is suitably proportioned to the desired cylindrical surface of gun fiute I1; that is, if the cylindrical duce the circumferential grooves and ridges 20.

The rake of the cutting teeth I8 is of substantial importance, and seriously affects the eftlciency and life of the tap. It has been found advantageous to shape the portion of the gun flute adjacent the teeth I8 to conform to the surface of a cylinder extending downwardly from the main ute I5 toward the end of the tap,.and a gun flute I'I of desirable contour for expelling the w chips in characteristic manner is provided when such cylinder lies tangent to a plane through the y tap axis intersecting the ute I6 and is of such diameter that its outer face is not substantially beyond a plane tangent to outermost threads I4 and parallel to said axial plane. This arrangement is shown in Figs. 2 and 3. In this construction however the rake of cutting tooth |80, which ordinarily makes the first cut in the work is substantially greater than that of the final cutting tooth I8f. The efciency of the tap depends to a substantial extent upon the effective operation of tooth I8f, whose apex is necessarily sharp. It is likewise important that the initial tooth I8a be given a proper rake, since its action particularly on relatively stringy metal is greatly enhanced thereby. A feature of the invention is to provide an arrangement in which both terminal teeth I8a and I8f may have the proper rake for their particular operations, the intermediate teeth IBIhaV- ing a suitable intermediate rake. Another feature is the accomplishment of this object while retaining the desirable contour of the gun flute I1 suitable for efiicient expulsion of the chips. Specifically, all of the teeth I8 may be given the same rake without seriously distorting the desired gun flute contour. i

. This may bey accomplished by employing in the gun flute a grinding, abrading or cutting device having an effective conical surface arranged with the smaller diameter portion operating on the final cutting tooth I 8f and the larger diameter portion eiective along the initial cutting tooth I8a. With this system the increased diameter adjacent the initial teeth may be designed to compensate for the longer arc of contact already described in connection with Figs. 2 and 3, so that the desired widening of the gun flute II toward the tap end will be retained and at the same time a substantially uniform rake of all of the cutting teeth I8 will be produced. This embodiment is illustrated in Figs. 4 and 5, employing the conical grinding wheel 22.

properly proportioning and and positioning the cylindrical grinding wheel 2 I relative to the cutting teeth I8 as indicated in Fig. 6. With this arrangement the'wheel corresponding to wheel VI9.is suitably located with its cylindrical surface lin nal'grinding position at the desired rake angle lin the zone of engagement with cutting teeth I5',

I8a and I8f, respectively. For instance, as lllustrated in Fig. 6, the tip threads have a rake alpha of about 20 while the root threads have a similar rake beta ofl about 20. While this arrangement permits the maintenance of a nearly uniforml rake or a predetermined variation in rake. between the end teeth, it also imposes restrictions on the size of the grinding wheel 2I' and the resulting proportions of the gun flute I1 and in some cases the wheel 2| would be required to be shifted laterally during operation.

While a preferred arrangement has been illustrated, and has been shown substantially in correct relative proportions in the drawing, numerous modifications may be introduced without departing from the scope of the invention as set forth in the claims. For instance, while a tap with two flutes isshown in Figs. 1-6J any desired practicable number of -flutes or the likemay be employed. Likewise, wheels 2I, 2l and 22 are not restricted to surfacing or polishing, but may be utilized to form or shapev the gun flute.

This is a division of my application Serial No. 204,489, filed April 27, 1938, now Patent No. 2,202,236 granted May 28, 1940.

I claim: Y

A method of formingutes in a tap which comprises cutting a main ilute along the tap and a gun flute extending downwardly from the main flute to the entering end ofthe tap, and'abrading the gun flute surface by means of a conical abrading wheel positioned with its base adjacent the end of the tap and forming the gun flute at progressively increasing diameters toward the end of the tap and having its-surface at a substantially constant angle to the radii extending from the tap axis to the apices of the end teeth of the tap so that the angles of rake of said teeth along said gun flute are substantially the same.

GLEN H. STIMSON. 

